System, transmitter, receiver, signal, method, for distributing services

ABSTRACT

A system for distributing a signal carrying a plurality of services, the system comprises: a transmitter for generating numbering information pertaining to the plurality of services, for including the numbering information into the signal, and for transmitting the signal, a receiver for receiving the signal, for retrieving the numbering information from the signal, and for numbering services of the plurality of services in dependence of the numbering information.

The invention relates to a system for distributing a signal carrying aplurality of services.

The invention also relates to a transmitter, a receiver, and a signalfor use in such a system.

The invention also relates to a method for distributing, a method fortransmitting, and a method for receiving, a signal carrying a pluralityof services.

A system as described in the opening paragraph is known from digitalnetworks such as a DVB-T network for the terrestrial and digitaldistribution of transport streams carrying a plurality of services, e.g.television programs. A network operator broadcasts the services using atransmitter that emits transport streams at a carrier frequency.End-users can experience the broadcasted content by using a receiverthat is coupled to the transmitter by a medium through which thebroadcast propagates. The receiver tunes to the appropriate carrierfrequency to receive the desired transport streams and the services. Theend-user typically selects at least one of the plurality of services toexperience. The receiver assigns a number to each service forease-of-reference by the end-user. This number is used in the userinterface of the receiver. The receiver may receive signals from severaltransmitters.

It is a disadvantage of the known systems that the user interface of thereceiver is affected by changes in the plurality of services or bychanges in the transmitter. The transmitter fading away or not operatingnormally may cause these changes. The network operators changing thetransmitted frequencies or moving the services to another frequency ornetwork may also cause these changes.

Another disadvantage is that the network operators can influence thenumbering of the services in the receiver only in a limited way.

It is an object of the present invention to provide for a system fordistributing a signal carrying a plurality of services that does notsuffer from the abovementioned drawbacks.

This object is realized in that the system for distributing a signalcarrying a plurality of services comprises:

-   -   a transmitter for generating numbering information pertaining to        the plurality of services, for including the numbering        information into the signal, and for transmitting the signal,    -   a receiver for receiving the signal, for retrieving the        numbering information from the signal, and for numbering        services of the plurality of services in dependence of the        numbering information.

By transmitting and receiving the numbering information, the numberingof the services in the receiver can be controlled by the transmitter,i.e. by the network operator controlling the transmitter. The system maycomprise or be part of a DVB-T network. The numbering information maypertain to certain aspects of the plurality of services, like adescriptor, a modification, a history, an indicator for a moved service,or an indication on how to number the service. Detailed examples of theinformation are included further below; see the tables and therespective text. The generation of the numbering information may beunder (manual) control of the network operator. Alternatively, thenumbering information may be created automatically.

The receiver may be part of a television set, a set top box, or astorage device like a video recorder. The receiver receives the signalcarrying the plurality of services and the numbering information. Thereceiver may be arranged to assign a number to each service received.The receiver may also be arranged to search for services. The receiveris arranged for numbering the services in dependence of the information.The numbering may be modified in response to an event. Examples of suchan event are described in detail below. The event may relate to thenumbering information being received, an end-user interacting with thereceiver, or a reception quality. The numbering of the services may beimplemented in software that is executed by a processor in the receiver.

The above object and features of the system, the transmitter, thereceiver, the signal, the method, and the computer program product ofthe present invention will be more apparent from the followingdescription with reference to the drawings.

FIG. 1 shows a block diagram of the system 100 for distributing servicesaccording to the invention.

FIG. 2 shows a flowchart of the method 200 for distributing servicesaccording to the invention.

FIG. 3 shows an example of a signal 110 according to the invention. Someof the functions or elements in the drawings may be implemented insoftware, and as such represent software entities, such as softwaremodules or objects.

Digital Terrestrial Television (DTT) networks as specified byDVB-Terrestrial offer a large number of digital television and radioservices 120, 121. Over time the networks evolve, offering otherservices. Also new DTT networks can be introduced. To assist the enduser in keeping track of new, moved or deleted services, aDVB-Terrestrial receiver 140 can be equipped with an ‘Automatic ServiceUpdate Installation’ function. The ‘Automatic Service UpdateInstallation’ function depends on signaling information such as ServiceInformation (SI) as distributed by DTT networks. The assignment ofpreset numbers 151, 152 to services 120, 121 is in dependence of theavailability of the ‘logical_channel_descriptor’ 320 in the NetworkInformation Table 310, which is part of the distribution 110. Thisleaves manufacturer specific solutions open, which are sometimes notdesired by DTT network operators.

Use of a first descriptor 340 may be used to obtain an improved‘Automatic Service Update Installation’ function in a DVB-T receiver.The first descriptor 340 may be transmitted in the Network InformationTable 310 (NIT). The first descriptor may be called “Automatic serviceupdate descriptor” and contains detailed information for DVB-T receiverson how to perform an Automatic Service Update Installation. An exampleof syntax and semantics of the first descriptor is given further below.

The use of a new linkage_type 350 may be used to signal a service 120,121 that has moved within a network or that has moved from a network toanother network. An example of syntax and semantics of the newlinkage_type 350 is given further below.

To give DTT network operators more control on the assignment of presetnumbers 151, 152, a second descriptor 360 may be used. The seconddescriptor 360 comprises a recommendation for receivers 140 on how toassign preset numbers to specific groups of services 120, 121. Thesecond descriptor 360 may be called “LCN reserved range descriptor” Thesecond descriptor may be transmitted in the NIT 310. An example ofsyntax and semantics of the second descriptor is given further below.

The syntax is based on tuples of a tag, a length and a value.

A DVB-T receiver may automatically update the list of installed servicesbased on service information being broadcast on DVB-T networks. A commonunderstanding between network operators and receiver manufacturers isneeded for a reliable automatic update installation feature in DVB-Treceivers.

From a receiver point of view an automatic service update installationfunction needs to detect changes in the service information delivered bythe received DVB-T network. This service information may be carried inNIT/actual and may be extended with NIT/other. Also SDT/actual andSDT/other contain service information. Here the focus is on serviceinformation carried in NIT/actual.

To be able to describe an automatic service update installation functionthe concept of a list of installed services in the receiver should beclear. A data model of a list of installed services is described later.This data model is only used as a reference and does not imply animplementation rule.

Triggers

The automatic service update installation function is supposed toexecute as a background task in the receiver. This means that it maylikely not disturb the viewing experience of the user. Also the user mayhave no direct control to start a service update installation function.

The service update installation function may be activated by either ofthe following triggers or a combination thereof:

-   -   A new version of NIT/actual 310 is received    -   The user tunes to a service 120, 121    -   The receiver 140 is switched to standby    -   A timer expires 160

An example of a combination is that the function is activated only inresponse to the timer expiring, while the timer is restarted with everyof the other triggers. The following will elaborate upon some triggers.

A New Version of Nit/actual is Received

When the system receives a new version of NIT/actual it can process thedata in NIT/actual to automatically update changes in the servicesprovided by the network described by this NIT/actual.

The table below gives an overview which data in NIT/actual is beingprocessed to detect changes in a network. delivery frequency service TSsystem list list LCN loop descriptor descriptor descriptor descriptor TSadded to network ● ∘ ∘ ∘ ∘ TS deleted from network ● TS assigned to newfrequency in ● ● same network Service added to the network ● ∘ Serviceremoved from the network ● ∘ Service relocated on another TS in ● ∘ thenetwork● a change in this data triggers the processing of the network changedefined in column 1.∘ this data is used for further processing of the network change definedin column 1.A change in the Transport Stream loop

The receiver inspects the transport stream (TS) loop of the new versionof NIT/actual to detect changes in the transport streams delivered bythe network. The following changes are identified:

-   -   1. A transport stream is added to the network when the TS loop        describes a transport stream that is not known by the list of        installed services in the receiver. The receiver 140 may        schedule a partial scan for the new transport stream to        determine the best-tuned frequency (using a delivery system        descriptor and a frequency list descriptor).    -   2. A transport stream is deleted from the network when the        transport stream is known by the list of installed services in        the receiver (and delivered by this network) and this transport        stream is not described in the TS loop. Services in the list of        installed services in the receiver that are received via the        deleted transport stream may be nominated for deletion.        A change in delivery system descriptor/frequency list descriptor

The receiver 140 inspects the delivery system descriptor and frequencylist descriptor to detect changes in the delivery parameters andfrequencies of transport streams known by the list of installed servicesin the receiver.

A transport stream is assigned to one or more new frequencies in thenetwork when the delivery system descriptor or frequency list descriptoris changed. The receiver may schedule a partial scan for the existingtransport stream to determine the best-tuned frequency. This can be thefrequency with the strongest signal or with a highest reception qualitymeasure.

A change in service list descriptor

The receiver 140 compares all service list descriptors in the newversion of NITactual with the list of installed services in thereceiver. The following changes are identified:

-   -   1. A service 120, 121 is removed from a network when the        service_id in the list of installed services is not listed in        the set of service list descriptors in the new version of        NIT/actual 310. The service may be nominated for deletion in the        list of installed services. This means that the service is not        physically removed from the list of installed services but is        kept so the receiver can keep track of it.    -   2. A service is added to a network when a new service_id is        listed in the set of service list descriptors in the new version        of NIT/actual. The service is added to the list of installed        services.    -   3. A service is relocated in a network when an existing        service_id is listed in a service list descriptor of another        transport stream description in the new version of NIT/actual.        The service properties are updated in the list of installed        services.        Assigning preset Numbers 150, 151 to new Services 120, 121

When a logical channel descriptor 320 is present in the new version ofNIT/actual 310, the new services that are added to the service list maybe automatically assigned to the preset number 150, 151 equal to thelogical channel number 122.

When the logical channel number of a new service is already in use byanother service in the list of installed services the preset number ofthe new service is resolved depending on the following situations:

-   -   1. The preset number is in use by a service nominated for        deletion. The receiver may detach the preset number from the        service nominated for deletion and assigns the preset number to        the new service.    -   2. The preset number is in use by an existing service and was        manually assigned to this preset number by the end user. The        receiver may assign the new service to another preset number in        a manufacturer dependent way.    -   3. The preset number is in use by an existing service from        another network. Since no new version of NIT/actual of the other        network is available the receiver is likely not able to resolve        this immediately. The receiver may assign a (temporary) preset        number to the new service. Only after the receiver is tuned to        the other network (user selects another service) the receiver        can resolve this based on the current version of NIT/actual of        the other network:        -   a. When the other network is not using the logical channel            number anymore the new service may be moved from the            temporary preset number to the preset number equal to the            logical channel number.        -   b. When the other network is still using the logical channel            number and refers to the identical service as the newly            added service (same service id's) then the receiver may            arbitrate which one of the services will have a preset            number assigned (making duplicate services invisible to the            end user).        -   c. When the other network is still using the logical channel            number and refers to a service different from the newly            added service (different service id's) the services may be            regional variants. The receiver may arbitrate which one of            the services will be assigned to the preset number equal to            the logical channel number. The other service will be            assigned to another preset number in a manufacturer            dependent way. The other service will be assigned to another            preset number in a manufacturer dependent way.            Note 1: The preset number conflict can also occur in more            than 2 networks. In those cases all involved networks should            be inspected to resolve the conflict.            Note 2: Arbitration which service will be assigned to the            preset number equal to the logical channel descriptor is            manufacturer dependent. A possible arbitration method is to            select the service with the best reception quality.

When no logical channel descriptor 320 is present in the new version ofNIT/actual, new services are assigned to free preset numbers in amanufacturer specific way.

A special case: A service moves to another Network

When the receiver, tuned to a specific network, has no access to actualupdates in other networks (the tuned network does for example notdeliver NIT/other) then a move of a service to another network can bedetected in two sequential updates. The order of detecting the twoindividual updates is arbitrary but has some influence on how thereceiver can react.

When a service moves from the tuned network to another network the newversion of NIT/actual will indicate that the service is deleted from thenetwork. There is no information about the destination of the serviceuntil the receiver is tuned to the other network that now contains themoved service. The NIT/actual will indicate that the service is added tothe network.

When a service moves from another network to the tuned network the newversion of NIT/actual will indicate that a service is added to thenetwork. The receiver may notice that the added service is a duplicateand arbitrates which one is assigned to a preset number. When the userselects this service the receiver can already locate the new location ofthe service without the need to know that the service was moved.

Therefore it is desired that a linkage descriptor 350 may be used toindicate a service move to another network.

A change in Logical channel Descriptor 320

When the logical channel descriptor 320 in the new version of NIT/actual310 indicates that existing services 120, 121 are rearranged to otherpreset numbers 150, 151, the receiver 140 may update the list ofinstalled services 120, 121 accordingly. Conflicts may be handled in thesame way as described above. Preset numbers of existing services may bereassigned prior to assigning preset numbers to new services in order toavoid conflicts with new services as much as possible.

When the receiver has scheduled a Partial scan for a Transport Stream

When a partial scan is necessary to find the best-tuned frequency of atransport stream this partial scan may be started when:

-   -   1. The user tunes to a transport stream that needs a partial        scan (by service selection). The partial scan may be done for        this transport stream only.    -   2. When the user switches the receiver in standby mode. The        partial scan may be done for every transport stream that needs a        partial scan.

During a partial scan the receiver may tune to all frequencies specifiedin the terrestrial delivery system descriptor and the frequency listdescriptor from the last known NIT/actual. The frequency with the bestreception quality may be set as the best-tuned frequency.

When no transport stream is received at all the partial scan may berepeated every time the user selects the transport stream.

The user Tunes to a Service

When the user tunes to a service 120, 121 by selecting a preset number151, 152 the receiver 140 may first tune to the transport stream thatdelivers the specified service 120, 121 and then select the service. Twospecific situations in this process may trigger the automatic serviceupdate installation function.

When a Transport stream cannot be Tuned

When the user tunes to a transport stream and the tuner cannot lock onthe transport stream at the specified frequency or when a signal loss isdetected the receiver may perform a partial scan to recover the requiredtransport stream.

When a partial scan cannot recover the required transport stream, thereceiver may attempt to tune to another transport stream in the samenetwork. When this succeeds the NIT/actual may be inspected to detectnetwork changes. When no network changes are detected the receiver mayinform the user that the selected service is temporary unavailable. Whennetwork changes are detected the receiver may update the list ofinstalled services.

An Alternative method to relocate a Transport stream after a FrequencyChange.

When the network transmitters have been reconfigured to otherfrequencies, a partial scan using the old frequencies may have noresult. To prevent the need for a full service installation thebroadcaster may advertise the new transmitter frequencies in a nextversion of NITactual 310 during the last period before the transmitterreconfiguration. A receiver may store the next version of NITactual inmemory and may use the new frequencies during a partial scan to find thebest-tuned frequency in the new transmitter configuration.

When the Selected service 120, 121 is not Available

When the user selects a service from the installed service list and thereceiver detects that the service is (or becomes) not available thereceiver may try a number of alternatives to tune the same service or asubstitute service.

The first alternative is to find the same service (same service_id) inthe list of installed services.

The second alternative is to find a service in the list of installedservices with an identical logical channel number.

When no alternative is found, the user may be informed that the serviceis not available.

The receiver is Switched to Standby

Regular Full Scans

It is desirable to perform regular full frequency scans (e.g. in standbymode, at least once a week) to enhance the ability to detect newnetworks.

Another descriptor is proposed with which a broadcaster may announcemajor network changes that require a full scan.

Subject: Implementation of Signalling for Automatic service updateFeatures.

Automatic service update Descriptor

The automatic_service_update_descriptor 340 may be carried in the firstloop of NIT 310. TABLE 1 Automatic service update descriptor Syntax No.of bits Identifier automatic_service_update_descriptor( ){ descriptor_tag 8 uimsbf  descriptor_length 8 uimsbf service_list_enable_flag 1 bslbf  partial_scan_flag 1 bslbf SDTother_flag 1 bslbf  reserved_for_future_use 5 bslbf }Semantics for the Automatic service update Descriptor

service_list_enable_flag: This 1-bit field indicates whether theautomatic service update function of the receiver can use theinformation in the service_list_descriptor carried in NIT/actual toupdate the user service list. If set to “1”, the receiver may be able torely on the information carried in the service_list_descriptors in thesecond loop of NIT/actual. If set to “0”, the receiver may check theSDT/actual before any service updates are processed in the user servicelist.

Note 1: When service_list_enable_flag is set to “1” the NIT may carry acomplete service_list_descriptor for every transport stream of thenetwork

Note 2: Even if the service_list_descriptors in NIT/actual contain acomplete list of services, SDT checking may be required. For examplewhen not every service can be received in all geographical areas coveredby the network, the SDT/actual may carry this information in theservice_availability_descriptor.

partial_scan_flag: This 1 -bit field indicates whether automatic serviceupdate function of the receiver can perform a partial scan based on thefrequency_list_descriptors in the second loop of NIT/actual. If set to“1”, a partial scan can be performed. If set to “0”, a partial scan isnot recommended.

Note: When partial_scan_flag is set to “1” the NIT may specify the fulllist of alternative frequencies for each transport stream of thenetwork.

SDTother_flag: This 1-bit field indicates whether the automatic serviceupdate function of the receiver can use the SDT/other tables to updatethe service list. If set to “1”, the SDT/other tables can be used toupdate the service list. If set to “0”, the use of 25 SDT/other is notrecommended to automatically update the service list.

Note: Use of SDT/other may increase the performance of the automaticservice update function. For a proper functioning the information inSDT/other should be complete for every transport stream in the network.Each SDT/other should contain the same information as SDT/actual of thecorresponding transport stream.

Linkage type 350 to Identify moved Services

A new linkage type “service move” may be defined for the linkagedescriptor. Linkage descriptors of this type may be carried in the firstloop of the NIT 310.

The “service move” linkage type 350 can be used to signal the move of aspecific service to another network. Additionally a service move withinthe same network can be signalled in case noservice_list_descriptor/frequency_list_descriptor is carried in thesecond loop of NIT and no SDT/other is available. TABLE 2 Automaticservice update descriptor Syntax No. of bits Identifierlinkage_descriptor( ){ <addition to existing linkage descriptor syntax> if (linkage_type == “service move”){   service_move_type 8 uimsbf  network_id 16 uimsbf   network_descriptors_length 8 uimsbf   for (i=0;i<N;i++){    descriptor( )   }  } }Semantics for linkage type “Service Move”

service_move_type: This is an 8-bit field specifying the type of servicemove: TABLE 3 Service move type coding service_move_type Description0x01 Service moved to another network 0x02 Service moved within thisnetwork 0x03 Service moved to a new network (see note) 0x04 to 0xFFreserved for future use

Note: When a new network is introduced, existing services are notnecessarily moved to this new network. It is also possible that the newnetwork only introduces new services. In this case the service_id fieldin the linkage_descriptor may refer to a service not yet known by thereceiver.

network_id: This 16-bit field identifies the Network that is deliveringthe service.

The following descriptors can be used in the descriptor loop of a“service move” linkage:

-   -   terrestrial_delivery_system_descriptor    -   frequency_list_descriptor        The combination of these two descriptors specifies all possible        frequencies where the service can be located.        LCN Reserved Range Descriptor

The LCN_reserved_range_descriptor 360 may be carried in the first loopof NIT 310. TABLE 4 LCN reserved range descriptor Syntax No. of bitsIdentifier LCN_reserved_range_descriptor( ){  descriptor_tag 8 uimsbf descriptor_length 8 uimsbf  range_type 8 uimsbf  lowest_preset_number10 uimsbf  highest_preset_number 10 uimsbf  reserved 4 bslbf }Semantics for the LCN reserved range descriptor

range_type: This is an 8 -bit field specifying the type of the range:TABLE 5 range type coding range_type Description 0x01 range for servicesnot allocatable on specified LCN 0x02 range for receiver equipmentspecific services 0x03 range for radio services 0x04 range for otherbroadcast services 0x05 to 0xFF reserved for future uselowest_preset_number: The lowest value of the range of preset numbers151, 152 used to allocate duplicate services 120, 121. Value may be inthe range 1 till 999.lowest_preset_number: The highest value of the range of preset numbersused to allocate duplicate services. Value may be in the range 1 till999.

The range_type indicates how the range is to be applied by the receiver140. If the preset number suggested by the LCN 320 of a service 120, 121is already occupied at a receiver 140, the receiver is instructed toassign the service to a preset number 151, 152 in the range specifiedfor which the range_type equals 0×01.

Receiver equipment specific services may be services that are local tothe receiver, like a gaming service.

A receiver may use a separate list of preset numbers for radio servicesand for tv services. To avoid a single number referring to both a radioservice and a tv service, the range specified with range_type 0×03 maybe used for assigning preset numbers to radio services.

It is noted that the above-mentioned embodiments illustrate rather thanlimit the invention, and that those skilled in the art will be able todesign many alternative embodiments without departing from the scope ofthe appended claims. In the claims, any reference signs placed betweenparentheses shall not be construed as limiting the claim. The word“comprising” does not exclude the presence of elements or steps otherthan those listed in a claim. The word “a” or “an” preceding an elementdoes not exclude the presence of a plurality of such elements. Theinvention can be implemented by means of hardware comprising severaldistinct elements, and by means of a suitably programmed computer. Inthe device claim enumerating several means, several of these means canbe embodied by one and the same item of hardware. The mere fact thatcertain measures are recited in mutually different dependent claims doesnot indicate that a combination of these measures cannot be used toadvantage.

1. A system (100) for distributing a signal (110) carrying a pluralityof services (120, 121), the system (100) comprising: a transmitter (130)for generating numbering information (122) pertaining to the pluralityof services, for including the numbering information (122) into thesignal (110), and for transmitting the signal, a receiver (140) forreceiving the signal (110), for retrieving the numbering information(122) from the signal (110), and for numbering services (120, 121) ofthe plurality of services in dependence of the numbering information(122).
 2. A system (100) as claimed in claim 1, characterized in thatthe numbering information (122) pertains to a history of the pluralityof services (120, 121).
 3. A system (100) as claimed in claim 1,characterized in that the numbering information (122) pertains to amodification of a service out of the plurality of services (120, 121).4. A system (100) as claimed in claim 3, characterized in that themodification comprises a frequency modification, a transport streammodification and/or a network modification.
 5. A system (100) as claimedin claim 1, characterized in that the numbering information (122)pertains to a change in the transmitting.
 6. A transmitter (130) for usein a system as claimed in claim
 1. 7. A receiver (140) for use in asystem as claimed in claim
 1. 8. A receiver (140) as claimed in claim 7,characterized in that the receiver is arranged for numbering services ofthe plurality of services (120, 121) in dependence on a receptionquality.
 9. A receiver (140) as claimed in claim 7, characterized inthat the receiver is arranged for numbering services of the plurality ofservices (120, 121) in dependence on a history of the plurality ofservices (120, 121).
 10. A receiver (140) as claimed in claim 7,characterized in that the receiver is arranged for numbering services ofthe plurality of services (120, 121) in response to an event.
 11. Asignal (110) for use in a system as claimed in claim 1, the signal (110)comprising a representation of the numbering information (122).
 12. Acomputer program product enabling a programmable device when executingthe computer program product to function as a receiver (140) as definedin claim
 7. 13. A method (200) for distributing a signal (110) carryinga plurality of services, (120, 121) the method comprising: (210)generating numbering information (123) pertaining to the plurality ofservices (120, 121); (220) including the numbering information (123)into the signal (110); (230) transmitting the signal (110); (240)receiving the signal (110); (250) retrieving the numbering information(123) from the signal (110); and (260) numbering services of theplurality of services (120, 121) in dependence of the numberinginformation (123).
 14. A method for transmitting a signal (110) carryinga plurality of services, (120, 121) the method comprising: (210)generating numbering information (123) pertaining to the plurality ofservices (120, 121); (220) including the numbering information (123)into the signal (110); and (230) transmitting the signal (110.
 15. Amethod for receiving a signal (110) carrying a plurality of services,(120, 121) the method comprising: (240) receiving the signal (110);(250) retrieving the numbering information (123) from the signal (110);and (260) numbering services of the plurality of services (120, 121) independence of the numbering information (123).